Ultra-high-frequency antenna assembly and parasitic array therefor



p 25,1967 H. GREENBERG ETAL 3,344,431

ULTRA-HIGH'FREQUENCY ANTENNA ASSEMBLY AND PARASITIC ARRAY THEREFOR 2 Sheets-Sheet 1 Filed Aug. 14, 1963 INVENTORS HARRY GREENBERG CHARLES ox. |u

BY QM M ATTORNEYS Sept. 26, 1967 Filed Aug. 14. 1963 H. GREENBERG ETAL ULTRA-HIGH-FREQUENCY ANTENNA ASSEMBLY AND PARASITIC ARRAY THEREFOR llllnh 2 Sheets-Sheet 2- INVENTOR HARRY GREENBERG CHARLES C.Y. LIU

BYZZM M ATTORNEYS United States Patent ULTRA-HlGH-FREQUENCY ANTENNA ASSEMBLY The present invention relates to antennas and particularly to antennas suitable for use in the ultra-high-frequency range of television broadcasting.

In that UHF range, encompassing channels 14 to '83 and extending over the frequency range of 470 megacycles to 890 megacycles, special problems are presented. One of the important problems is that of attenuation. As is well known, as the frequency of transmission increases so does the attenuation between the transmitter and the receiving antenna, so that for reasonable amounts of broadcast power it becomes more and more important that the gain of the antenna be increased to compensate for the increased attenuation. In the UHF television broadcast range, as a practical matter, the gain of an ordinary dipole is insuflicient for this purpose and must be enhanced.

A well-known way of enhancing the gain of a dipole is to place a reflector behind it. This produces a small increase in gain but is limited in effect. A further wellknown way of increasing the gain is to use parasitic elements called directors in front of the antenna. For each properly designed and spaced additional element placed in front of the antenna a slight additional amount of gain is provided. The result is the so-called Yagi array, which in its common form consists of a single active element with a series of parasitic director rods arrayed in front of it, and generally with a reflector behind it. However, the Yagi array suffers from the disadvantage that the gain is fairly sharply dependent upon the relationship be tween the lengths of the parasitic elements and the op erating frequency. Thus, if the frequency of operation is changed, as is necessary in switching from one channel to another, gain is decreased unless the lengths and spacings of the parasitic elements are changed correspondingly. This can become an extremely troublesome problem when it is realized that up to parasitic elements may be required for adequate gain, and for optimum performance all of these elements would have to be adjusted simultaneously in length and spacing upon change in channel.

The present invention is directed toward antennas generally of the Yagi type which are economical in manufacture and which in large measure solve or avoid the above problems of the conventional UHF Yagi array.

According to one aspect of the present invention, a novel active or dipole element is provided having a special configuration which, particularly when in association with the novel parasitic element array of the present invention, provides a highly desirable gain versus frequency characteristic and obtains good gain over the entire band of UHF television broadcasting.

Another aspect of the present invention relates to novel structures of parasitic elements which are both economical to manufacture and which are easily adjustable in the field to provide enhanced antenna effectiveness.

These and other advantages of the present invention will become more fully apparent upon consideration of the following detailed description of a preferred embodiment of the present invention, taken in conjunction with the annexed drawings in which:

FIGURE 1 is a plan view of a preferred embodiment of the complete antenna assembly of the present invention;

FIGURE 2 is an end elevation view, viewed from the reflector end of the antenna assembly of FIG. 1;

FIGURE 3 is a side elevation view thereof;

FIGURE 4 is a plan view of the active or dipole element thereof;

FIGURE 5 is a cross-sectional view taken along line 55 of FIGURE 1 and particularly showing the downlead connection;

FIGURE 6 is a fragmentary view of a part of the parasitic array, adjusted for the lowest frequency of operation;

FIGURE 7 is a similar fragmentary view of the parasitic array adjusted for the highest frequency of operation;

FIGURE 8 is a fragmentary view of the parasitic array showing a modified form of provision for adjustment.

The antenna of the present invention is formed of three principal units, namely, an active element 11, a reflector element 12, and a parasitic array 13, having two sections 13a and 13b. Each of these elements is mounted on a cross-arm or cross beam 14 in the manner to be described, the cross-arm 14 being preferably a channel-shaped member whose cross-section is seen best in FIGURE 5, although any suitable shape of cross-arm and any appropriate structure for supporting the principal elements 11, 12, 13 may be used.

The reflector assembly 12 is generally of conventional form, and comprises a series of horizontal conductive rods or tubes 16 suitably supported on a vertical conductive cross-piece 18 which in turn is secured to the cross-arm 14 in any desired manner, as by means of a bracket 20.

Spaced forwardly of the reflector assembly 12 a distance appropriate for reflector action over the UHF range, is the active element assembly 11 shown in FIGURES 1 and 4. This active element 11 is fabricated from a single sheet of conductive material as by punching, stamping, cutting, or the like, and its configuration and proportioning forms a novel and highly useful arrangement,

As seen in FIGURE 4, the active element 11 is in the form of a hollow elongated diamond-shaped plane sheet having a pair of opposed acute vertices 22 and a pair of obtuse vertices, one of which has a gap 24 therein. The length of the diamond-shaped dipole element is approximately three to four times its width to form a fairly narrow diamond configuration. The diamond-shaped configuration is hollow and has a central opening 38 of oval form to provide fiat strip-like sections 32 and solid end pieces 34. While the opening 38 in the dipole element 11 is indicated as oval in shape, this is not essential to the operation of the element, which can also attain substantially similar results with other shapes of opening, such as formed by combined straight and curved lines, or straight lines alone, forming a polygonal shape. The sections 32 may be strips of uniform or varying widths, as may be desired.

The opening 38 is illustrated as symmetrically disposed relative to the diamond outline of the element. However, this is not essential; shifting the opening laterally relative to the diamond outline (i.e., as by making the left strips 32 thinner and the right strips 32 thicker) will merely result in a different antenna impedance, as may be desirable in some stages.

For reasons which are not entirely understood, an important relationship in connection with the effectiveness of the dipole element 11 for its intended purpose is the relation between the overall length of the dipole element between the acute vertices 22, and the length of the opening 38 within the dipole element. It has been found empirically that, for optimum operation over the operating frequency band, the length of the dipole element overall should be approximately twice that of the opening. Practical and effective results are also obtained if this relationship is departed from to some extent, for example, ratios as low as 1% or as high as 2% will produce useful results.

The dipole element 11 has holes 40 adjacent the ends of strips 32 on either side of the gap 24. These holes 40 serve to connect to an insulating bracket 42 having a U- shaped portion 44 and side flanges 46 which are apertured in correspondence with the holes 40 in the active element 11. Suitable connecting and terminal devices, such as screws 48 with wing nuts 50 pass through the matching holes 40 of the dipole element 11 and the holes in flanges 46 of the bracket 42 to secure the ends of strips 32 to bracket 42 and additionally to connect the two ends 52 of a down-lead transmission line 54 to the dipole element 11. The bracket 42 has a central aperture 56 by means of which the bracket 42 and its connected dipole element 11 are connected to the cross-arm 14, as by means of a threaded or other fastener 58, so as to be supported by cross-arm 14. The dipole has a tab extension 28 at the center of the unbroken side of the dipole element, and at an electrically neutral point, permitting tab 28 to be mounted on and electrically connected to the cross-arm 14 (and by a fastener passing through hole 30 of tab 28 and an aligned hole of cross-arm 14) without affecting the electrical operation of the dipole element.

While the dipole element has a fixed length it operates satisfactorily over the entire approximately 2 to l frequency range of UHF television broadcasting, because of its configuration which gives it broad-band characteristics, especially in association with the present particular director array, as described below.

An important factor in the operation of the active dipole element is its use of the solid end portions 34. While the theory of operation is not certain, it is believed that this arrangement, together with the approximately 2 to 1 ratio of overall length to length of opening 38, produces a broad-banding effect.

As indicated above, the parasitic director array 13 of the present invention is made in two sections 13a and 13b. This is solely for convenience of mounting and in order to accommodate the vertical mast 15 and the clamping arrangement 17 by which mast 15 is secured to the horizontal cross-arm 14. With other mounting means, the director array 13 may be made in a single continuous arrangement.

The parasitic array section 13a will be described first in detail as representative of both sections 13a and 13b. It is formed of two flat, horizontally disposed, elongated, conductive sheets 60, 62 of a particular form to be described, which when juxtaposed in the manner to be described provide a multiplicity of parasitic directors adjustable in length over the desired frequency range.

The sheet 62 (which in FIGURE 1 is indicated as the topmost sheet) is formed with a continuous base portion 64 and a multiplicity of pointed tapered extensions 66, preferably but not necessarily symmetrical about axes transverse to the length of sheet 62. Sheet 60 therefore has one straight edge and one saw-toothed or serrated edge, and will be referred to as a serrated sheet. The second sheet 60 similarly has a continuous base portion 68 and a corresponding multiplicity of pointed tapered extensions 70. The two serrated sheets 60 and 62 are preferably identical to one another but mounted overlapped and in opposition so that the tapered points 66 of one are opposed to the similar tapered points 70 of the other along axes transverse to the lengths of the serrated sheets 60, 62, thus forming together a doubly serrated elongated strip. The base sections 64, 68 lie on and extend along the length of the cross-arm 14 to which they are secured and conductively connected, so that they form essentially a single doubly serrated elongated strip lying substantially in a horizontal plane and with a median line lying on and extending along the cross-arm 14.

In this way each opposed pair of tapered points 66, 70 forms essentially a diamond-shaped conductive structure, and the two serrated sheets 60, 62 taken together provide a multiplicity of such diamond-shaped structures each having a major axis transverse to the cross-arm and parallel to the major axis of the active element 11. The frontmost diamond next to mast 15 and clamp 17 is split along its longer axis to form a half-diamond 76.

On the front side of the mast 15 and the clamp 17 which support the cross-arm 14 and the various elements thereon, is a second section 1313 of the parasitic director array, which is essentially of the same construction just described with respect to section 13a. The leftmost or rear director 89 of array section 1312 is formed as a half-diamond mating with the half-diamond 76, and these two half-diamond elements are electrically connected by conductive straps 78. The length of the conducting straps 78 is chosen s that the spacing between the tips of half-diamond element 76 and the half-diamond element 80 is the same as the spacing between the tips of the diamond-shaped directors of sections 13a and 13b, so that elements 76 and 80 serve as director elements on either side of mast 15 and without disturbing the regularity of spacing of all the director elements. In other respects, array section 131) is the same a section 1311, being formed of two serrated elongated conductive sheets 60a, 62a symmetrically disposed along cross-arm 14 and overlapped to form effectively a single doubly-serrated sheet or strip, with a sequence of diamond-shaped elements.

It will be understood that the director array 13 is divided into sections 13a, 1311 only for the mechanical convenience of locating the mast 15 and clamp 17 as shown. For other mounting arrangements for the cross-arm 14, the director array may be made as a single section, of appropriate length, having the desired number of diamondshaped director elements for the required gain and directivity.

In electrical functioning, each diamond-shaped configuration formed by an opposed pair of points 66, 70 constitutes one parasitic director element for the complete antenna assembly. As is common with such parasitic directors, the center points are electrically neutral and may be connected directly to the grounded cross-arm 14. Th distance between successive directors is fixed by the manner in which the sheets 60, 62 (or 60a, 62a) are fabricated and is designed to give a proper spacing over the operating band. In the present assembly, the director spacing is maintained uniform for the entire area, at an appropriate value between A and ,5, of any wavelength in the operating range. As many directors are used as h desired gain may require, 22 being used in a representative example.

Each of the serrated sheets 60, 62 (or 60a, 62a) is provided with slots 72, 74 at appropriate points along its length. In the case of parasitic array section 13a there are two slots, one adjacent each end, and in the case of section 13b there are three slots, one adjacent each end and one approximately at the center of the longitudinal dimension. Each of these slots is located in the base portion of the respective sheet 60, 62, extending transversely of the axis of the parasitic array. For purposes of maintaining structural strength it is preferable that the slots be located along the major axis of the corresponding diamond shapes forming the directors. Extending transversely through both slots of the superposed serrated sheets 60 and 62 are fasteners 75 which also extend through respectively aligned apertures in the cross-arm 14. These fasteners may for example be screws and wing nuts. By means of these slots 72, 74 the length of the individual diamond-shaped director transverse to the cross-arm 14 can be simultaneously adjusted, as is illustrated in FIG- URES l, 5 and 6. FIGURE 5 shows the situation in which the serrated sheets 60 and 62 are extended laterally to the utmost extent, so that the lengths of the diamond-shaped director elements are maximum. FIGURE 6 shows another adjustment for which the lengths of the diamondshaped director elements are minimum. It will be seen here that the base sections of the serrated sheets 60, 62 overlap to the least extent in FIGURE 5 and to the maximum extent in FIGURE 6, while in FIGURE 1 they overlap to an intermediate extent.

The arrangement just described provides a simple method for simultaneous adjustment of the lengths of the director elements, which would normally be done at the time the antenna is installed.

As is well known, in different sections of the country the Federal Communications Commission has allocated different channels for TV broadcast on the UHF band or range. In installing the antenna of the present invention, the lengths of the director elements should be adjusted to provide optimum operation for the highest frequency channel which can be received in the locality where the antenna is being installed. This is done by suitably separating the serrated sheets 69, 62 and 60a, 62a to the proper point. It is a property of the present antenna assembly that all lower-frequency channels will be found to have effective antenna operation, particularly as to gain. The reason for this is not fully understood but it is believed to be as follows. The director array just described appears to have a gain characteristic electrically similar to that of a low-pass filter, with gain increasing gradually with frequency until a relatively sharp upper-frequency cutoff, and with the property that the higher the cutoff frequency is, the lower will be the average gain over the operating band. Accordingly, by adjusting the antenna to cut off just above the highest channel to be received, maximum gain it attained over the range of operating channels up to the cutoff frequency. While the gain changes somewhat with the overall bandwidth, sufliciently to justify the desirability of adjusting the cutoff point, even over the entire range up to channel 83 the present antenna assembly affords improved gain over conventional antennas, over the entire operating band.

The improvement is believed in part due to the fact that, as the operating band is narrowed, the adjusted length of the directors is the proper length for the higher channels in the operating band, and raising the gain for them as well as for lower channels. This more than overcomes the increased attenuation at the higher channels due to increased frequency of transmission. In addition, the special diamond shape of the directors is believed to make their effect less sensitive to change in frequency. As a result the present invention provides as a practical matter an improved uniformity of gain versus channel frequency and a higher average gain over the operating range.

The present parasitic array 13 especially cooperates with the dipole element 11 to contribute further to desirable broad-banding by which desired uniformity of signal is obtained. From FIG. 1 it will be seen that the serrated sheets 60, 62 overlap the right-hand leg of dipole 11. The amount of this overlap will vary as the overlap between serrated sheets 60, 62 is varied. Thus, for the higher frequencies, where serrated sheets 60, 62 are overlapped to a greater degree, the overlap of the parasite array over the dipole is greater, and vice versa for lower frequencies. This overlap tends to modify the effective length of the dipole element, and thereby further contributes to uniformity of output over the entire operating range.

As indicated above the length of the diamond-shaped director elements is adjusted in the field at the time of installation. To aid the installer in doing this, the cali brated scale shown at 82 may be associated with the slots 72, 74 and marked suitably by channel numbers so that the installer can adjust the length of the diamondshaped elements to correspond to the highest frequency channel being broadcast in that area.

FIGURE 7 shows' a modified arrangement in which the slots 72, 74 are provided with a plurality of extensions or notches extending along the length of the cross-arm 14 and indicated illustratively as four in number. These notches can serve as a rough approximation to the scales 82, and can aid the installer in setting the director length to any of four predetermined positions corresponding to the range or channels to be received. Alternatively, in the arrangement of FIGURE 7 adjustment between the notches 84 is still possible when desired by leaving the fastener 76 in the main slots 72, 74 instead of in the notches 84.

While the dipole element and director array of the present invention may be mounted and supported in many ways within the scope of the invention, the above description has indicated a highly desirable form of the invention which is easy to fabricate, to mount, to assemble and to adjust.

While it will be understood that in addition to the UHF television broadcast range the invention is useful for other UHF and similar ranges of frequencies, for illustrative purposes the following dimensions are given with respect to one form of the invention found to be highly useful for the UHF television broadcast range:

Inches Length of reflector element 16 19 Length of reflector cross-piece 18 20 Overall length of active element 11 11 /2 In sheets 60a, 62a 14 Length of serrated sheets 6%, 62 24 Length of serrated sheets 60a, 62a 44 Overall width of serrated sheets 60, 62, 69a, 62a 5% Spacing between tips of adjacent director elements 3% Maximum director length 10 /2 Minimum director length 7% Distance between half-diamonds 76, 8t 3%,

These dimensions are illustrative only, and may be varied, depending upon the intended operating range of the antenna.

It will thus be seen that instead of providing a multiplicity of conventional rod-type director elements, each having individual mounting and individual dimensioning of its length and spacing, the present invention provides a Yagi antenna assembly where the adjustable director array is formed from two punched or otherwise simply fabricated sheets which can very easily be mounted and adjusted, thereby providing substantial economies in manufacture and improvements in uniformity of operation over the entire operating band.

It will be understood that where adjustment of the lengths of the director elements is not desired, sheets 60, 62 or 60a, 62a may be combined into a single integral sheet, of doubly serrated configuration, providing the consecutive array of substantially diamond-shaped director elements.

In the theoretical Yagi array, the directors have individually different lengths, which generally increase from the front of the array toward the rear. In the present invention, where desired, this variation in director length can readily be attained, either by varying the point-tobase dimension of serrated sheets 60, 62, 69a, 62a along their length, or merely by overlapping sheets 60, 62 or 60a, 62a in a tapering or non-parallel fashion. However, to obtain the major benefits of the present invention it is not necessary to .go to the trouble of such refinements.

Although the parasitic director array has been described as flat and made from conductive sheets, it may Z have substantial and non-uniform thickness, as when cast or machined of conductive material. Preferably however, in such case, the thickness preferably tapers off from a maximum at the center to a minimum at the edges.

It will be appreciated that the foregoing description applies only to one embodiment of the present invention and that other forms of the invention will readily be conceived or designed by those of ordinary skill in the art. The present invention is accordingly not to be limited to the specific illustration given, but is defined solely by the appended claims.

What is claimed is:

1. A parasitic element array for an antenna assembly comprising a pair of identical horizontal elongated serrated conductive sheets, each having a straight edge extending the length thereof and an opposite edge having a series of equal-sided, identical, equally spaced, triangular projections forming a saw-toothed configuration, said sheets being mounted in parallel overlapping relation with their respective triangular projections in opposed relation to form a plurality of equal, substantially diamondshaped, parasitic elements extending transversely to the long dimension of said sheets, and means for adjusting the amount of overlap of said serrated sheets to adjust the lengths of said diamond-shaped parasitic elements transverse to said long dimension.

2. A parasitic element array for an antenna assembly comprising a pair of identical elongated serrated conductive sheets, each having a straight edge extending the length thereof and an opposite edge having a series of triangular projections forming a saw-toothed configuration, said sheets being mounted in parallel overlapping relation with their respective triangular projections in opposed relation so that each pair of opposed projections forms a substantially diamond-shaped parasitic element extending transversely to the long dimension of said sheets, and means for adjusting the amount of overlap of said serrated sheets to adjust the lengths of said diamond-shaped parasitic elements transverse to said long dimension.

3. A parasitic element array for an antenna assembly comprising a pair of elongated serrated conductive sheets, each having a straight edge extending the length thereof and an opposite edge having a series of triangular projections forming a saw-toothed configuration, said sheets being mounted in overlapping relation with their respective triangular projections in opposed relation so that each opposed pair of projections forms a substantially diamondshaped element and means for adjusting the amount of overlap of said sheets to adjust the lengths of said diamondshaped elements.

4. A parasitic element array for an antenna assembly comprising a pair of elongated serrated conductive sheets having the same configuration, each sheet having a base, said sheets being mounted with their bases in overlapping arrangement and with the tips of the serrations of one disposed oppositely to those of the other, whereby each oppositely disposed pair of serrations forms a parasitic element, and means for transversely adjusting said two sheets relative to one another to adjust the separation between each opposed pair of serrations and thereby to adjust the lengths of said parasitic elements.

5. A parasitic element array for an antenna assembly comprising a fiat elongated doubly serrated conductive structure having a pair of opposed edges extending the length thereof, each said edge having a series of equalsided, identical equally spaced, triangular projections forming a saw-toothed configuration, the triangular projections along said two edges being in respective opposed relation with each opposed pair of projections forming a substantially diamond-shaped parasitic element extending transversely to the long dimension of said structure, and means for simultaneously adjusting the lengths of said diamond-shaped elements transverse to said long dimension.

6. In combination, a parasitic element array for an antenna assembly comprising an elongated doubly serrated conductive structure having a pair of opposed edges extending the length thereof, each said edge having a series of equally spaced pointed projections forming substantially a saw-toothed configuration, said projections along said two edges being in respective opposed relation, with each opposed pair of projections forming a parasitic element having a shape tapering toward each end and extending transversely to the long dimension of said structure; and an active element spaced rearwardly of said array, said active element comprising a folded dipole having a wider dimension at the center than at the ends thereof.

7. An array as in claim 6, wherein said pointed projections have the same shape.

8. A parasitic element array for an antenna assembly comprising an elongated doubly serrated conductive structure having a pair of opposed edges extending the length thereof, each said edge having a series of pointed projections forming substantially a saw-toothed configuration, said projections along said two edges being in respective opposed relation, with each opposed pair of projections forming a parasitic element having a shape tapering toward each end and extending transversely to the long dimension of said structure, each of said pointed projections being formed by two straight edges, said edges being respectively forwardly and rearwardly inclined with respect to the length of said conductive structure.

9. An array as in claim 3 wherein each pair of edges of said projections is symmetrical about a perpendicular to said length.

10. An antenna assembly comprising a horizontal crossarm, a reflector element mounted adjacent one end of said cross-arm, an active element mounted on said cross-arm and spaced forwardly from said deflector element, and a horizontal parasitic director array mounted on said crossarm forwardly of said active element; said active element comprising a pair of horizontally disposed solid conducting portions, each having two straight outer sides meeting at an acute angle and forming a vertex, said vertices facing away from one another and said two solid portions being symmetrically disposed with respect to each other and said vertices, an integral strip extension of each of the two straight sides of each of said solid portions, one strip extension from one of said solid portions and one strip extension from the other of said solid portions integrally joining at an obtuse angle to form a side vertex, the other strip extensions extending toward one another at an obtuse angle but ending short of one another to form a gap, and a pair of terminals for said dipole element connected respectively to the adjacent ends of said other strip extensions, the ratio of the length of said dipole element from one acute vertex to the other being approximately three times the width of said dipole element from said side vertex to said gap and the said length being approximately twice the distance between said solid portions, said active element being disposed in a horizontal plane with said gap facing to the rear, and a transmission line connected to said terminals, said parasitic director array comprising a pair of identical horizontal elongated serrated conductive sheets, each having a straight edge extending the length thereof and an opposite edge having a series of equal-sided, identical, equally spaced, triangular projections forming a saw-toothed configuration, said sheets being mounted in parallel overlapping relation with their respective triangular projections in opposed relation to form a plurality of equal, substantially diamondshaped, parasitic elements extending transversely to the long dimension of said sheets, and means for adjusting the amount of overlap of said serrated sheets to adjust the length of said diamond-shaped parasitic elements transverse to said long dimension, said parasitic element array being in partially overlapping relation to said side vertex.

11. An antenna assembly comprising a horizontal crossarm, a reflector element mounted adjacent one end of said cross-arm, an active element mounted on said cross-arm and spaced forwardly from said reflector element, and a horizontal parasite director array mounted on said crossarm forwardly of said active element, said active element comprising a pair of horizontally disposed solid conducting portions, each having two sides meeting at an acute angle and forming a vertex, a conductive strip joined to and forming an extension of each of the said two sides of each of said solid portions, one strip from one of said solid portions and one strip from the other of said solid portions being joined at an obtuse angle to form a side vertex, the other strips extending toward one another at an obtuse angle but ending short of one another to form a gap, whereby said solid portions and strips form a structure tapering from the center toward both said first vertices and with a central opening, and a pair of terminals for said dipole element connected respectively to the adjacent ends of said other strips, said active element being disposed in a horizontal plane with said gap facing to the rear, and a transmission line connected to said terminals, said parasitic director array comprising a pair of elongated serrated conductive sheets, each having a straight edge extending the length thereof and an opposite edge having a series of triangular projections forming a saw-toothed configuration, said sheets being mounted in overlapping relation with their respective triangular projections in opposed relation so that each opposed pair of projections forms a substantially diamond-shaped element, and means for transversely adjusting said two sheets relative to one another to adjust the separation between each opposed pair of serrations and thereby to adjust the lengths of said parasitic elements, said parasitic element array being in partially overlapping relation to said side vertex.

12. An antenna assembly comprising a horizontal crossarm, a reflector element mounted adjacent one end of said cross-arm, an active element mounted on said crossarm and spaced forwardly from said reflector element, and a horizontal parasitic director array mounted on said cross-arm forwardly of said active element; said active element comprising a dipole element for an antenna assembly comprising a sheet of conductive material having a substantialiy diamond-shaped outer configuration and an inner opening symmetrical therewith, said configuration having a pair of opposed acute-angle end vertices and an intermediate pair of opposed obtuse-angle vertices, one of said obtuse-angle vertices being interrupted by a gap connecting said opening to the exterior of said element, the overall length of the dipole element being related to the length of the opening by a ratio of approximately 2, and a pair of transmission line terminals connected to said element at opposite sides of said gap, said active element being disposed in a horizontal plane with said gap facing to the rear, and a transmission line connected to said terminals, said parasitic director array comprising a pair of elongated serrated conductive sheets having the same configuration, said sheets being mounted with their bases in overlapping arrangement and with the tips of the serrations of one disposed oppositely to those of the other, whereby each oppositely disposed pair of serrations forms a parasitic element, and means for transversely adjusting said two sheets relative to one another to adjust the separation between each opposed pair of serrations and thereby to adjust the lengths of said parasitic elements.

13. An antenna assembly comprising a horizontal crossarm, a reflector element mounted adjacent one end of said cross-arm, an active element mounted on said cross-arm and spaced forwardly from said reflector element, and a horizontal parasitic director array mounted on said crossarm forwardly of said active element; said active element comprising a body of conductive material having a horizontal projection of its outer configuration tapering toward both ends from the middle and having an inner opening therewithin, said configuration having a pair of opposed acute-angle end vertices and an intermediate pair of opposed obtuse-angle vertices, one of said obtuseangle vertices being interrupted by a gap connecting said opening to the exterior of said element, and a pair of transmission line terminals connected to said element at opposite sides of said gap, said active element being disposed in a horizontal plane with said gap facing to the rear, and a transmission line connected to said terminals, said parasitic director array comprising an elongated doubly serrated conductive structure having a pair of opposed edges extending the length thereof, each said edge having a series of pointed projections forming substantially a saw-toothed configuration, said projections along said two edges being in respective opposed relation, with each opposed pair of projections forming a parasitic element having a shape tapering toward each end and extending transversely to the long dimension of said structure.

14. An antenna assembly comprising a horizontal crossarm, a reflector element mounted adjacent one end of said cross-arm, an active element mounted on said cross-arm and spaced forwardly from said reflector element, and a horizontal parasitic director array mounted on said crossarm forwardly of said active element; said parasitic director array comprising a pair of elongated serrated conductive sheets having the same configuration, said sheets being mounted with their bases in overlapping arrangement and with the tips of the serrations of one disposed oppositely to those of the other, whereby each oppositely disposed pair of serrations forms a parasitic element, and means for transversely adjusting said two sheets relative to one another to adjust the separation between each opposed pair of serrations and thereby to adjust the lengths of said parasitic elements, said parasitic element array being in partially overlapping relation to said active element.

15. An antenna assembly comprising a horizontal cross- 3113, 8. reflector element mounted adjacent one end of said cross-arm, an active element mounted on said cross-arm and spaced forwardly from said reflector element, and a horizontal parasitic director array mounted on said crossarm forwardly of said active element; said parasitic director array comprising an elongated doubly serrated conductive structure having a pair of opposed edges extending the length thereof, each said edge having a series of pointed projections forming substantially a saw-toothed configuration, said projections along said two edges being in respective opposed relation, with each opposed pair of projections forming a parasitic element having a shape tapering toward each end and extending transversely to the long dimension of said structure, said parasitic element array having a portion rearward of the forwardrnost portion of said active element.

16. An antenna assembly comprising a horizontal crossarm, an active element mounted on said cross-arm and a horizontal parasitic director array mounted on said crossarm forwardly of said active element, said parasitic director array comprising a pair of elongated serrated conductive sheets having the same configuration, each sheet having a base, said sheets being mounted with their bases in overlapping arrangement and with the tips of the serrations of one disposed oppositely to those of the other, whereby each oppositely disposed pair of serrations forms a parasitic element, and means for transversely adjusting said two sheets relative to one another to adjust the separation between each opposed pair of serrations and thereby to adjust the lengths of said parasitic elements.

17. An antenna assembly comprising a horizontal crossarm, an active element mounted on said cross-arm and a horizontal parasitic director array mounted on said crossarm forwardly of said active element; said parasitic director array comprising an elongated doubly serrated conductive structure having a pair of opposed edges extending the length thereof, each said edge having a series of equally spaced pointed projections forming substantially a sawtoothed configuration, said projections along said two edges being in respective opposed relation, with each opposed pair of projections forming a parasitic element having a shape tapering toward each end and extending transversely to the long dimension of said structure; said active element comprising a folded dipole having a wider dimension at the center than at the ends thereof.

18. An array as in claim 17, wherein said pointed projections have the same shape.

19. An antenna assembly comprising a horizontal crossarm, an active element mounted on said cross-arm and a horizontal parasitic director array mounted on said crossarm forwardly of said active element; said parasitic director array comprising an elongated doubly serrated conductive structure having a pair of opposed edges extending the length thereof, each said edge having a series of pointed projections forming substantially a saw-toothed configuration, said projections along said two edges being in respective opposed relation, with each opposed pair of projections forming a parasitic element having a shape tapering toward each end and extending transversely to the long dimension of said structure, each of said pointed projections being formed by two straight edges, said edges being respectively forwardly and rearwardly inclined.

2t). An array as in claim 19 wherein each pair of edges of said projections is symmetrical about a perpendicular to said length.

21. An antenna assembly comprising a horizontal crossarm, an active element mounted on said cross-arm and a horizontal parasitic director array mounted on said crossarm forwardly of said active element; said active element comprising a horizontal elongated folded dipole having a front-to-rear dimension at the center thereof tapering toward each end, and a gap at said center and facing toward the rear of said antenna assembly, a pair of terminals connected to said dipole, one on either side of said gap; said parasitic director array comprising an elongated horizontal doubly serrated, unitary conductive structure, partially overlapping said dipole.

22. An antenna assembly comprising a horizontal crossarm, an active element mounted on said cross-arm and a horizontal parasitic director array mounted on said crossarm forwardly of said active element; said active element comprising a horizontal elongated folded dipole having a front-to-rear dimension at the center thereof tapering toward each end, said parasitic director array comprising an elongated horizontal doubly serrated, unitary conductive structure.

23. An integral planar dipole element comprising a pair of horizontally disposed solid conducting portions, each having two straight outer sides meeting at an acute angle and forming a vertex, said vertices facing away from one another and said two solid portions being symmetrically disposed with respect to each other and said vertices, an integral strip extension of each of the two straight sides of each of said solid portions, one strip extension from one of said solid portions and one strip extension from the other of said solid portions integrally joining at an obtuse angle to form a side vertex, the other strip extensions extending toward one another at an obtuse angle but ending short of one another to form a gap, and a pair of terminals for said dipole element connected respectively to the adjacent ends of said other strip extensions, the ratio of the length of said dipole element from one acute vertex to the other being approximately three times the width of said dipole element from said side vortex to said gap, and the said length being approximately twice the distance between said solid portions.

24. A dipole element as in claim 23 further including an insulating member joining the ends of said other strip extensions and spanning said gap, and a tab extension integral with said dipole element at said side vertex, whereby said dipole element is adapted to be mounted in a horizontal plane on a horizontal cross-arm by said tab extension and insulating member.

25. A planar dipole element comprising a pair of horizontally and oppositely disposed solid conducting portions, each having two straight outer sides meeting at an acute angle and forming a vertex, said vertices facing away from one another and said two solid portions being symmetrically disposed with respect to each other and said vertices, a strip joined to and forming an extension of each of the two straight sides of each of said triangular portions, one strip from one of said solid portions and one strip from the other of said solid portions being joined at an obtuse angle to form a side vertex, the other strips extending toward one another at an obtuse angle but ending short of one another to form a gap, whereby said solid portions and strips form a generally diamondshaped structure with an elongated central opening, and a pair of terminals for said dipole element connected respectively to the adjacent ends of said other strips, the length of said dipole element from one acute vertex to the other being approximately twice the length of said opening.

26. A planar dipole element comprising a pair of fiat horizontally disposed solid conducting portions, each having two sides meeting at an acute angle and forming a vertex, a conductive strip joined to and forming an extension of each of the said two sides of each of said solid portions, one strip from one of said solid portions and one strip from the other of said solid portions being joined at an obtuse angle to form a side vertex, the other strips extending toward one another at an obtuse angle but ending short of one another to form a gap, whereby said solid portions and strips form a structure tapering from the center toward both said first vertices and with a central opening, and a pair of terminals for said dipole element connected respectively to the adjacent ends of said other strips.

27. A dipole element for an antenna assembly comprising a sheet of conductive material having a substantially diamond-shaped outer configuration and an inner opening symmetrical therewith, said configuration having a pair of opposed acute-angle end vertices and an intermediate pair of opposed obtuse-angle vertices, one of said obtuse angle vertices being interrupted by a gap connecting said opening to the exterior of said element, the overall length of the dipole element being related to the length of the opening by a ratio of substantially between l% and 2 /1, and a pair of transmission line terminals connected to said element at opposite sides of said gap.

28. A dipole element for an antenna assembly comprising a sheet of conductive material having a substantially diamond-shaped outer configuration and an inner opening symmetrical therewith, said configuration having a pair of opposed acute-angle end vertices and an intermediate pair of opposed obtuse-angle vertices, one of said obtuse-angle vertices being interrupted by a gap connecting said opening to the exterior of said element, the overall length of the dipole element being related to the length of the opening by a ratio of approximately 2, and a pair of transmission line terminals connected to said element at opposite sides of said gap.

29. A dipole element for an antenna assembly comprising a body of conductive material having a horizontal projection of its outer configuration tapering toward both ends from its center and having an inner opening therewithin, said configuration having a pair of opposed acute-angle end vertices and an intermediate pair of opposed obtuse-angle vertices, one of said obtuse-angle vertices being interrupted by a gap connecting said opening to the exterior of said element, the overall length of the dipole element being related to the length of the opening by a ratio of substantially between 1% and 2%, and the ratio of said length to the effective width of said diamond configuration being approximately between three and four and a pair of transmission line terminals connected to said element at opposite sides of said gap.

39. A dipole element for an antenna assembly comprising a body of conductive material having a horizontal projection with an outer configuration tapered from the center toward each end and having an inner opening symmetrical with said outer configuration and a gap in said configuration substantially at said center, and a pair of terminals connected to said body respectively on opposite sides of said gap, the overall length of said dipole element being related to the length of said opening by a ratio of substantially between 1% and 2%, said configuration having a pair of opposed acute-angle end vertices and an intermediate pair of opposed obtuse-angle vertices, one of said obtuse-angle vertices being interrupted by a gap connecting said opening to the exterior of said element.

31. A dipole element for an antenna assembly comprising a body of conductive material having a horizontal projection of its outer configuration tapering to- Ward both ends from the middle and having an inner opening therewithin, said configuration having a pair of opposed acute-angle end vertices and an intermediate pair of opposed obtuse-angle vertices, only of said obtuseangle vertices being interrupted by a gap connecting said opening to the exterior of said element, and a pair of transmission line terminals connected to said element at opposite sides of said gap.

References Cited UNITED STATES PATENTS 2,518,736 8/1950 Wheeler 343806 X 2,644,091 5/1953 Middlemark 343819 X 2,958,868 11/1960 Okamura 343-795 2,981,951 4/ 1961 Wickersham 343-795 3,110,030 11/1963 Cole 343-795 ELI LIEBERMAN, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,344,431 September 26, 1967 Harry Greenberg et a1.

t error appears in the above numbered pat- It is hereby certified the hat the said Letters Patent should read as ent requiring correction and t corrected below Column 14, line 3, after "only" insert one Signed and sealed this 15th day of October 1968.

(SEAL) Attest:

EDWARD J. BRENNER Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer 

22. AN ANTENNA ASSEMBLY COMPRISING A HORIZONTAL CROSSARM, AN ACTIVE ELEMENT MOUNTED ON SAID CROSS-ARM AND A HORIZONTAL PARASITIC DIRECTOR ARRAY MOUNTED ON SAID CROSSARM FORWARDLY OF SAID ACTIVE ELEMENT; SAID ACTIVE ELEMENT COMPRISING A HORIZONTAL ELONGATED FOLDED DIPOLE HAVING A FRONT-TO-REAR DIMENSION AT THE CENTER THEREOF TAPERING TOWARD EACH END, SAID PARASITIC DIRECTOR ARRAY COMPRISING AN ELONGATED HORIZONTAL DOUBLY SERRATED, UNITARY CONDUCTIVE STRUCTURE. 